This invention relates to a method of producing a bracket and a gear box of an electric motor, and more particularly to a method of connecting the bracket integrally with the gear box formed of an electrically insulating synthetic resinous material. Also the present invention concerns a metal mold used with such a method.
A conventional fan is an example of a machine having an electric motor with a gear box. Such fans involve typically conventional fans. Those fans have been operated to effect ventilation through a plurality of rotary blades mounted at one end of a motor shaft rotated at a high speed while swinging the main fan body several times per minute through a gear disposed within the gear box formed integrally with the motor bracket to engage a worm disposed at the other end of the motor shaft, thereby to decelerate the rotation of the motor shaft.
In such a structure, by which the main motor body swings through the gears as described above, the gear box and the motor bracket formed integral therewith have been required to have both high dimensional accuracy and high strength. In order to fulfill such requirements, the bracket and gear box have been previously formed by die casting aluminium or zinc and the resulting castings have been subjected to after-machining conducted by a machine tool used exclusively for this purpose. This has resulted in the following disadvantages:
(a) Because aluminum or zinc is used as the material, harmful gases are evolved from the material melted at an elevated temperature, for example, about 800.degree. C., during the die casting operation. PA1 (b) Due to the use of a die casting technique, the resulting castings have such low dimensional accuracy as to require after-machining. Therefore the castings must be passed through a special machine tool capable of machining the castings with a machining accuracy of from 1/100 to 1/1000. In this case, scores of machining steps are required and the machining time becomes long. PA1 (c) In order to increase the mass producibility thereof, the special machine tool requires an extensive site for its layout. A rotary type special machine requires only a narrow floor area, but the machining of concentrated lots requires the use of several special machine tools, thus resulting in an increase in costs to be recovered.
From the foregoing it is seen that the bracket and gear box of a fan have been high in cost due to the additional steps added.
Accordingly, it is an object of the present invention to provide a new and improved method of producing a bracket and a gear box of an electric motor inexpensively as a result of existing equipment being used to mold the gear box without the necessity of machining the resulting molding.
It is another object of the present invention to provide a new and improved metal mold to be used in such method.